_  _ 

PHOTOROPISMS    "'I?H--tt03fdeHR<MATTtrXT(mTnnr"TTn^r5'  'AWVOLTOX. 

«e. 


.          S  tr  <t*.f*-.. 


+<-  /o  • 
ANNIE  LtAY   KURD. 


Subraitted  3*. partial  fulfillment  of  the  requirements 
for  the  degree  of  Doctor  of  Philosophy. 

University  of  California 


April    26,    1918. 


— /- 

/• 


OHZBHTATIOBS  ABB  PHOTOTROPISH8  IB  FUCU8  ABB  TOLTOZ 
WITH  HDBOCHHOJI&21C  LIGHT  OF  XQUAL  IH7HB8ZTZB8. 


ABBIB 


Submitted  in  partial  fulfillment  of  tb§  requirements 
for  the  degree  of  Doctor  of  Philosophy. 

University  of  California. 


April  26,  1916. 


/. 

PHOTOTROPIST'lS  WITT  T'ONOCTOOMATIC  LIG"T    IN  FUCUS   Alii)  VOLVOS. 


The  -nower  of  light  stimuli  to  produce  orientations  an  a 
/$r"opism3  is  a  phenomenon  which  has  been  widely  demonstrated  in 
both  the  plant  ana  animal  kingdoms.  ^ot  only  canfi  unilateral 
direct  movements  and  rrowth  out  in  some  srecies  of  r'-jnts,  name-* 
ly  ^quisetum,  Fucus,  90t-  Puccinia_,and  related  forms,  it  can 
establish  the  direction  of  the  first  cleavage  plane  of  the  ger- 
minating snore.  Since  in  such  cases  the  cell  on  the  shaded  side 
of  the  s^ore  becomes  the  rhizoidal  cell.  the  polarity  of  the 


plant   is    determined   irrespective   of   gravit.,-  . 

In  any   attempt    to    discover    t    e  mechanics    of   such  tropistic 
reactions,the  first   problem  is    to   find  what  wave  lengths    of 
light   are   responsible,    and   to  what    extent   they  are  a  function 
of   the  quality   of   the  stimulus/apart    from  its   quantity   or   inten- 
sity.   This,    then,    is    the  purpose   2$*J^ec7E££3ent'   investigation. 

^f^tL     fl^A-jeJLxJl-    T%    ^fc^t.   *>--L#&&i4^tM™%*^'  ,5^^»   SL&brvJL^-'i*)  <x*d  b  ~ 

^&.,,&f>&fi   reviewing   trie  literature  ***H&«i[Diological    experiments 

'  >^U-      *s~.0.i&-.     t^CS^rdf 

with  monochromatic  light  one  is  struck  by  fehe  abaanoo  of  quauti 


ave  records    of  -either    the  quality  w  tne   interisity   of   the   ill- 
umination.  -It   ia   tfr-woll   known   f;^ct   that  "Tae   ordinary   li^ht 
filters    used   to    obtain   rnonochtomatic   lig":t    transmit    not    only 

tho^e  vive  lengths  which  predo  ;iiu  .  t.t?    i  i        ive    t  .e   color    to   the 


screen,    but    rlso   othearts   of   the  spectrum  .thariresence   of 
can  be  detected  only    by  a   spectroscopic  analysis.  Vor    example, 
certain   results   are  frequently  ascribed   to  blue  light  with  no 
record   of   just   what   range    of    the   soectrum  was   used   nor   what 
"ave  lengths    other   than   the  predominating  ones  were  acting. 

'mother   source   of   inaccuracy  has   been   the  neglect   or   over- 
sight   of    the  great   variation   in   the  intensity    or   quantity    of   ra- 
diant   energy   transmitted    by   tjie   color    screens.   Biological 


.XO^IOV  CFiIA   BUO'JT  MI    VOIJ  OITAMOHHOOMCT'  TTTIW  eM 


;£   enoiJ'B.Jngi'io   sojjboarr   oJ    iJnrni^B   Jrfgil  lo    i9«.roa  orfT 
ni   bs^JBi^anomab   \;l9biw  nssd   earC  rfoirfw  nonsmonsprq  a   ei 


"  I 

iB'igJ'Blinu  nnso   ylno   Jo;;    .ei  oJb^nxx    iBmin;-    i-ru?   d'n^Icr  er*3   rf^ocf 


,eJrislT   "•  o    gsios-re   SPITOS   ni   iut    rf.twoT:     bnB   ecfnsmsvom 
^i    .emto'i   bsJelsi  briB  BinioouT  bn."  .euou'?    .nr 
lo   enslq  saavsalo   Jeii'J  9r^^   1o   noi^osixb   s 
9i>ie  bsbarfa  arf^   no    IIso   arf^    ese^o  rloue   ni   sonic!    .9ioae 

1o   ^JiiBlog  srfJ    Ilso    iBbiosirfi  gnd1    89Hioo9d   gao^e   er'.i   "io 

.v^iVBig   1o   9vi^o9qe9Tii   bgnimis^gb    ei 
rfoue   lo    ajini-i'Dy  J    i9voosifc    oJ    Jgnig^.^B  Yflfi 

/  fcl  er"  ?  enoi 

, 


experimenters  have  fot   he  most  part  failed  to  take  into 

i 

sideration  "he  fact  that  the  quantity  as  well  as  the  quality 

of  the  light  stimulus  varies  with  the  different  colors  and 
that  the  former  variable  must  be  eliminated  before  results 
can  be  attributed  to  differences  in  wave  length  alonei  Quite 

recently  (/y/Y  )such  work  has  been  aone  end  published  with  the 

die 


statement  thst^  results!  are  Qualitative  -eniy  becau-e  there  is 
no  way  of  comparing  lights  of  different  colors  as  to  amounts  & 

,_  <»tC*tx*-^e-     /* 

of  radiant  energj  .  kowev-er  there  have  been  several  methods  de~ 

A 
vised  by  means  of  which  the  relative  intensity  of  monochro- 

matic lights  van  be  measured. 

The  first  exact  work  of  this  nature  was  done  by  itniep 
and  Minder  C^°f).  They  usea  e  blue  and  a  red  color  screen  and 
a  green  solution  with  sunlight  as  the  source  of  light. 

XX>t&4 

The  wave  lengths  to  which  each/we^e  transparent  "/ere  known;; 
and  the  energy  behind  eacHi  was  determined  ny  means  of  a  therme- 
pile  and  a,  d'Arsonval  galvanometer.  The  interference  of  the  ±« 
long  heat  rays  w.-is  prevented  by  inserting  a  water  layer  in 
a  parallel  sided  container  between  tne  thermopile  and  the 
source  pf  light. 

Day  (/?/(  },  obtained  light  of  known  wave  length  by  mean 

of  a  spectfcum  from   ."ernt  Glower^s  formed  by  e  carbon 
bisulfide  prisu  and  cut  down  by/a  diaphragm  witn  narrow  ver- 

tical slits  whicn  could  be  adjusted  so  as  to  permit  any  de- 

sired region  of  tne  spectrum  to  be  used.  In  t-iis  adjustment  p 
spectroscope  w;-s  used  to  determine  the  exact  range  of  wave- 
lengths passing  through  the  plit.in  each  of  the  four  illumin- 
attions  used,  ---  red,  yellow,  gfeen,  and  blue.  He  measured 
intensity  of  each  with  a  Boys  r:  diomicromet,  er,  •  nd  balanced" 
them  by  varying  the  number  of  glowers  employed  in  the  lamps. 

"hus  there  was  one  glower  for  tne  red  light  light,  two  for  the 
yellow,  and  three  fot  the  green  ajid  biue. 


('?"  J 
Laurens  in  an  investigation  of  the  reactions  of  amphibians 

used  these  sane  metnods  and  the  same  ^ppnratus  for  the  quanti 
tave  analysis  oi-  the  monochromatic  light  he  u-ed^  ard  for  bnlanc- 
ing  then  with  respect  to  their  relative  intensity. 

Gross!  Ifi2)  also  used  these  snrne  methods  in  determining 
the  reactions  of  Arthropods  to  raonocnromatic  light. 

An  instrument  has  been  devised  by  I'.acDougal  and  Gpoehr.  (   ) 
which  ner-sures  the  total  radiant  energy  of  any  light  in  terras  of  1 
its  dissociation  effect  on  a  photosensitive  substance.  This  is 
measured  by  a  galvanometer,  "he  advantages  in  the  use  of  this 
"photoelectric  cell"  are  said  to  be  its  extreme  sensitiveness  t% 
the  wave  lengths  of  the  blue  end  of  the  spectrum, arid  the  fact  thst 

its  action  in  ligi-t  isHraore  nesrly  that  of  the  organism  than  that 

v 

of  any  othor  light  measuring  instruments  available. 

There  have  been  therefore  three  different  methods  worked  ot 
out  for  biological  experiraentsf or  the  quantitoive  analysis  ofi 
light  stimuli;  viz.,  those  of  Kniep  and  Hinder,  Day,  and  of 

^ racUoupiJ  and  Sooehr.  The  interesting  apparatus  of  Patte 

add  of  I.oeb  and  Northrut)  wherebya  quantitave  measurement  of  the  re- 
action of  organisms  subjected  to  two  beams  of  light  of  different 
intensity,  is  obtained.  The  measurement  is  in  terms  of  the  angular 
deflections  from  an  initial  path  of  locomotion.  The  same  methods 
might  be  ar^olied  to  work  with  colored  lights.  A  quantitative  measur- 
ment  of  the  greater  effectiveness  of  one  spectral  region  over  another 
of  equal  intensity  might  be  measured  by  the  angular  deviation  of  the 
rath  of  a  motile  organism  from  a  line  perpendicular  to  a  line  connect- 
inp  the  two  sources. 


All    of    these  methods   with   the    exception    of    those   of  i'nien   and 
inder    involve   special    a^^aratus    often   not    easily   available.    It   was 
aecessaty   for    fH  e   -rurroses    of    this    investigation   to   find   a   simpler 

of   accomplishing   the   sa-ne   results,    '"his    report    therefore      is 
concerned  "/ith   t'vo   rro  ultras;    first,    a  means    of   making   th  r:   intensity    of 
monochromatic    light    outlined      with    a    act    of    light    filters    equal; 
second,    a   comparative   study    of    the   tronisma    obtained  with    differ- 
rant  ™''ive   lengths   when    the   intensity   variable   in    eliminated.    The  nar- 

^henomena    chosen   for    this    study   are   t^  e  rower    of   monochro- 
matic  lights    to    (I)    establish   the   rolurity    of   ^ucus      sror el incs    and 
:,he   origin  and    consequent    direction    of    the  rhizoids;     (2)    to   nro- 
iuce   the  negative   rhototr -^ism    of    t1   n  rhizoid;    (3)    to   direct    the  move- 
icnt??    of   1rolvox. 


,    Ar>r«aratus   and  rethods   for   Exposure   to  Monochro- 
matic Light    of   Equal    Intensity. 


As    biologocal   science   oec  ones  more   exact  with   the   tend- 
eouce   the   expression   of  natural   -phenomena   to  mathematical    form- 
it    is    obviously    essential    to   define   stimuli  of   all    sorts   ouant- 
Ltatively.    Indefinaite   or   incomplete  records    of   light   stimuli    can 
10   longer    bo  attributed    to    the   lack    of  means    of   measuring   them   be- 
:aune  access    to  a   spectroscore  ano   thermopile  make   it   possible   to 
inalyae  any   light   qualitatively   ana   quantitatively. 


•anyq   put;   uaajj'    yif^.   qcoj   soaij^.   PUB    '/HOTESA" 

i/q.    aoj   O/A$    'q.u><TT   3-if^TT   psj  a;;^    aoj      i  auo    BUM  s-istf,    ..a 

•SUIT,  i   &;-;';    ui    •j;..jCoy<v  o    frsfl  o    jaqt.r  l-'uijCa  A 

peou'ui«q   pu      '  jc-'_e;:oaoT'  :oip  .a   e/!<  /.'q.  |  su,-  •..  UT 

.    paant,    c-)>  •      s    *atiiq  pun    'u.  '..oitsfi.    'pa.r   ---    'patm 

anoj   e^q.    jo   i;oi.o   uf^ti      ;  m      3.   ^uTut; 

jo   ef.'uij  ::a    oi'Cj.   aufisja^cjp    oq.  potm  B  ./.i   oaooaojQ.0 

•j  :;  ii   q.    u       -       .;n   eq    oq    raij^oa^l  jo   uo  ; 

-.  in.'-'ad   or4    su   Ofci   pa^an  ruoo    I.OTXIM  s 

-j-  |     |   '  .:  •  I       •.:/:'      u/.v   r;    |   no    pll;;    f'Sfc-: 

uo(\j-t;o     .    £<\  p-at.uoj    ..aao/^oio  •.;    a  j  utigq.o8.  s   u   jo 

g  suuot-  /!q   i{-_l:usT   9.J  IT    peuj«q.qo    ( 

.  T   t:d  eo^nos 

ai{^  PITB   etT^o'-'^^'U^    &-  ^    uocs^aq  ao-.-.-pc^uoo   [  -spys 
Uf    .re/lBi    ,:05.«M  u   ??uTq.J8eut   A"q  po^.  OA8jd   e   M  £/!<:      ^} 
oi   s  ;!}.   jo  eouajajjeq-uj   ei[i    •aa^eraoukiAio'J   T>AUOSJV,P    u  pu>:   s: 
u   ^o   su«su  yCq  pauTiae^op   Btm  ^c;o   puxtfsq   XSjeuo    9t{q. 
8js/..  ^uejHdauua',   aaaa  r.O'ua  ipyqM  o^   eq^guai   yA«/u 


•q.t£3fT  jo   aojnos   &i[^    s«  ^^Sftunt  tiq.T^   *uoTq.nxos    uaaa, 

• 
PUB   uaajoe    joioo   pej    i   ;u      eniq    .;    ,vasn  Jwifci    •(       •)    aaput;.  pun 

/!q.  auop   e«^  ean^ou  sfq,    jo   yLaOM     ^ot^.e 


eq 

. 
jo   A^Tfiue^uT   SAf^Biaj  eipj.   UOTI{<.,  jo   sueen  /!q  pesiA 

°  .-J     JO 


g  s^unonre  o-;    ^,    S.TOIOO   q.uajajjip   jo    B^trSfi  5?ufJxc^oo    jo  -^BA\  oq 
B-p"8joir^   e.-nebsq.  ^iuo   8ATq.(.^TiBnb 

t[^T^  poqsfiqnd  pu<;   auo;     uoaq    sutj 

8q.tri")  suoit;  i^!?uat  OAV.M  ut  BaouejajjTP  o;.  pa^riq-pja^f;  sq  u  .0 
s^insaj  aaojaq  pa^-jufUTTe  eq  ^sn1  8-[q«xj>JA  .letiijoj  at{^  ^em 
pu«  saoioo  q-uaaajjfp  ai^  i{^TM  safxuA  snimuf^e  m^TT  3^  J° 


-v>  u  3'. 

There  are  two  methods   for   obtaining  monochromatic   light   for 
biological    experiment/S  •'— .  ---the  projection   of  a  snectrum  upon 
the  yijH/y/i^X  organisms    or  <s    of    filtered  lir-'ht    passed   through 
a   colo      screen. The  former    i  .3    t"ieo    etically   the   tHMrtr  for    exact  ir 
work  but    technical   difficulties   such  as    the  limited  dispersion 
and     low   intensity  make  it   impractical   for   7iany   investigations. 
Light    filters    of    glass    are    the   :r.ost    convenient   "leans    of    se- 
curin,-  approximate!  oc   r     ;    I  LC   li—'t   when  unilateral   ill- 

umination  is   desired.    Ordinary   color   screens    transmit   too  wide 
a  range   of  wave  lengths   for    exact  T.vork      and  at   present   there  «t» 
are  very   f  w     iv';ose  lir'it   is    of   sufficient  homogeneity  .The    uest 
ia    the  Wratten  filter   screen,    made   in  London,      <"hich   consists    o 
of   a     1       '     -al-'tine  film  between    two    p/lass   platesVacDougal   and 
Sr>oehr(l9l7)    have   described   some   colored  glass    screens    designed 
by   them  for  biological   work,     but   the  range  of  wave  lengths    to 
which   they  ar-e   transparent    is    considerably   greater    than  for 
the  Wratten  filter. 

In   the  experiments    to  be  described,    seven  Wratten     light 

filters  were  used   ,     each   of  which  was   fitted  as   a  window   in   the 

•fy 

end  of  a  dak  b  .x.  i-lach  transmitted  only  a  narrqw  range  of 

-ave  lengths  but  all  together  they  embraced  the  whole  of  the 
visible  spectrum.  The  wave  lengths  to  which  each  screen  was 
transparent  ^ev* determined  by  testing  tie  lipht  transmitted  by^ 
each  with  a  direct  wtsion  spectroscope  with  a  wave  length  scale 
attached.  Thus   the  quality  of  the  light  stimulus  acting  in 
each  box  is  accurately  known. 


iirq.   PU«   use..  ?oj   so  .lift.   PUB    ' 

I   PSJ  w«    J°J      •<k°T»   suo   e«M  SJSXT 

o    joqu-  u   &Tf:     S)UT^J   A  o-ft 


nhe  source  of  light  oest  adapted  i'or  use  with  filters  for 
which  all  the  wave  lengths  of  the  visible  spectrum  nre  required 

^-w-vox-^ 


is  the  electric  ?<rc.  The  advantages  of  fts  use  .-; re, that  all 

filters  aan  be  u^ed  in  each  exposure,  insuring  identical  condition? 
of  temperature,  constancy  of  illumination,  etc.  The  disadvantages 

are  several.  In  the  first  place,  the  intensity  is  constantly  chang- 
ing as  the   carbonslburn  and  the  arc  gets  longer.  r/orse,  the  lessen- 
ing of  the  intensity  nay  not  be  the  sane  for  all  the  wave  lengths. 
In  the  second  place,  fluctuations  in  the  current  cause  large  vari- 
ations in  the  intensity.  In  tjje  third  place,  unless  an  ifafefefa&J- 
automatically  adjusted  arc  is  available,  it  is  necessary  to  adjust 

the  carbons  by  hand  every  five  to  fifteen  minutes^,  anfl  when  an 
eight  hour  illumination  is  desired, tt$A entails  considerable  inconven- 
ience. 

The  dark  boxes  were  10x13  en. find  8  era. high, in  one  end  ofe. 
which  a  hole  was  cut  so  that  one  of  the  light  filters,  6  x 6  cm. 
might  be  fitted  into  it.  The  boxes  were  made  light  tight  with 


tightly  fitting  covers,  and  were  painted  black  inside  to  guard 

for  uhe  cultures 

against  reflections  within  the  box.  The  dishes  used  were  made  of 

r\ 

microscope  slides  cemented  together  with  ainc  eement  so  as  to  make 
shallow  oblong  dishes  7.5x2.5  cm.  and  1  cm.  deep.  It  was  deemed 
necessary  to  use  such  flat  sided  dishes  in  order  to  prevent  posrible 
complications  from  reflected  and  refracted  light  in  the 


curving  sicleB   of   *»  round   dieMeo.    In   order   to   axrose  more      -        - 
than   one  dish     **=***&  behind   each  screen   Bo   that  none  would  be 


shaded  by*  another,    a  rack  was  made   to  fit   inside   the  box  with  ^ 

cleats   projecting   inward  from  the,  ends   so   that   three   dishes   c/culd  - 

he   elipped  into   it   one  above  the   other.The  light   .entering   through 
the   screen  at   the  end   of    the  box  ,    fell    equally   on   the   one   exposed 
side   of   each   of   the   three   dishes.      The  rack   containing  the   dishes 
could  be   easily  lifted   out   and  carried  to   the  microscope  for    exam^C 
ation  without   dicing   the  ,^^  ^^^-^^ 

The   spectrosccpic  analysis   of   the  light  passing   the  screens 
determine,   definitely   the  quality   of   light   entering   each  box.    It   is 
at   once   evident   that   the   quantity   or   intensity   of   light      behind 
filte«**««.   placed  at   #*£W*  equal    distances   from   the   source,    ^ 
vari33,both  because   the  intensity   of   light    transmitted  by  the  differ* 
ent   screens   is   dif^erent,and  because  the   different   colors  are  not 
radiated  by   the  arc  with   equal   intensity .This  being  the  case   ,    dif- 
erences    inrf  results   obtained  behind   the   screens  .could  not   be  attri- 
buted  to   differences   in   the  ^^^^^^^^^  __ 
energy  of  *&  colored  lights   ift^the   thermopile  and  sensitive  gal 

vSnometer.,  The    thermopile   is  very  sensitive   to   tne   energy  of 

/\ 

any  ether  vibtations  whether  they  be  the  longer  infra-red  or  so- 
called  heat  rays, or  the  shorter,  actinic  rays^of  the  spectrum. 

The  method  worked  out  for  ^eliminating  the  intensity  variable 
in  the  use  of  the  filters  employed  for  thtsr investigations,  consisted 
in  finding  the  distance  «*  from  the  light  source  at  which  each  box 
with  its  colored  window  should  be  placed  in  order  that  the  intensity^ 

as  indicated  by  the  deflection  of  the  galvanometer  when  tho  opeft- 

the  filter 
Qnd  Of-  the  thermopile  was  exposed  to  the  light  behind  &  ,  was 

in  each  case. 

It  seems  necessary,  on  account  of  the  questions  which  have 
been  raisedjduring  .he  course  of  this  work,  to  stsfe  here  that  the 
thermopile  is  equally  sensitive  to  the  energy  of r  the  red  and^he  vio- 
let ens  of  .he  spectrum,  and  is,  therefore,  an  accurate  measure 


of  the  total  amount  of  light  acting  behind  each  color  screen. 

.  ie  true  ueeauue  lEhe  difference  between  hent  and  light  is  only  a 

-r-  ^^ 

ter  of  wave  length. -i^.  ±a  truo  thtct  (the   thermopile  measures  jj7  in 

terms  of  the  electric  current  produced  by  a  difference  in  temperat- 
ure of  the  exposed  and  unexposed  junctions;  but  it  does  so  by  vir- 
tue of  the  fact  that  the  energy  of  whatever  vibrations  fall  upon 
it  be  thtfy  long  and  therefore  heating  in  their  physiological  ef- 
fect or   short  and  therefore  only  perceived  ad  light, is  converted 
into  heat  energy  upon  being  absorbed  by  the  exposed  junction  of  the 
thermopile.  In  other  words,  the  ligh-  of  the  blue  end  of  the  spec— 
1rum  produces  an  electromotive  force  much  less  than  that  of  the 
infra-  red  but  no  less  measurable. 

The  instrumetfnta  ur  td   in  the  enejjy  calibration  of  these 
screens  were  Si  ariffin^T1  ™  +  "™  table  thermopile  with  junctions 
of  bismuth  and  Hwrt^SSv  and  a  moderately  sensitive  galvanometer 
(d'Arsonval)  .^BsdaP  electric  arc  similar  to  the  one  later  used  in  * 
the  experiments  themselves  nas  the  source  of  light*  The  thermopile  -•** 
with  the  open  end  screened  by  on,e  of  ;the  lighjt  f  J.^exp,  was  / 


exposed  to  the  light  until  the  galvanometer  indicator  reached 
a  maximum  deflection  which  took, ordinarily^sbout  thirty  second^. 
The  number  of  divisions  through  which  the  spot  of  light  re- 

^^j-a^a    JU^a-frJL^-ca-fQ    *x*/  ~X-i^e,    *>-^<*-&e—. 

fleeted  from   the  galvanometer  mirror.was   noted. This   was   repea't" 
ed  six   times  and  the  average   deflection  recorded.    The   other 
filte^rs  were  then  used  in   turn   to   screen   the  thermopile  t 
and   thermopile  and  screen' moved  to      such  ^   distance 'rrom   the 
arc    that    the   displacement^  of    the  galvanometer  &3&&   indi-      ^ 


cator      opt*'*  approximately   equal.    This  -rdi3tan.c«'was ^.al.so  j^^^y 
for   the  ui'icnjroGne.d   thermopile^  which  rerres  en  red 


the  removal    of   the   control    from  the  source. For   the   experiment 
the  quantity   of   light  used   can  be  varied  for   the     whole  set  ^ 
of   screens   by   multiplying   or    dividing   these  distances   by 
the  same  numbervandthe  intensity   infall    the   boxes  will   remain 
equal.    The  actual    amount    o£     lisht    in   candlepowers    can  be 


measured  by  means    of   a  photometer.    Then   from   the   law   of   in- 

* 

verse   squares,    viz.,    that    the    intensity      of   li<*ht   per   unit 
surface  varies   inversely  as    the  aquare   of  t^  ft.  distance  from  -B 
the   source   ,    the   intensity  at   any   distance   from   the  arc   can 
be   computed. 


r 


The   calibration   oT~nTe\screens  was   repeated   seven   times 
or   until    satisfactory   checks    of   the   distances   were   obtained. 

some    thermopiles    of    less    rapid  action    than    the   one  used 
here,    it   «^/        in    impossible      to   get    results    oy   waiting  for 
the  galvanometer   indicator   to   come   to   a  steady  fftate.In     such 
a   case      the   deflections   produced  by    exposure      to   the  ligh^'""' 
for   equal    intervals   of   time   can   be   compared.   A  series    of 
measurements      f£om  five   second    exposures  agreed  very  well 
with   those   obtained  by   the  other  mejjthod, 


TABLE  SITC'VINr, 


LIGHT  FILTERS^) 


?ROM  AN 


TKAlOaTT2DARB  EQUAL. 


Filter  No.  Wave-   lengths        Color 

70  6600-^-7000   A.U.      Red 

71  6200-6800  A.U.      Red 


Distance  from   light 
320    cm. 
275    cm. 


72 

5900-6200 

Orange          23( 

73 

5600-5900   " 

Yellow          25( 

74 

5200-5609   " 

Green           28( 

75 

4700-5200   " 

Blue            25( 

76 

4000-4700   " 

Violet          25( 

\ 

Control 

,'JTe.         34( 

;e  the  same"  effect  it  migTTE  oe  tne  resort  or  a  general  inten- 
iy  gradiant;  if  only  the  blue  ligh<;  is  effective,  the  problem 
one  of  a  chemical  effect;  if  only  the  red  it  might  be  assumed 


in.  TROPIRTIC  REACTIONS  TO  MONOCHROMATIC  LIGHT  IN  FUCUS 

SPORELINGS. 


The  power  of  external  factors  to  determine  the  polarity  of 
a  germinating  spore  is, without  doubt,  the  power  to  orient  the  spin- 
dle of  the  first  dividing  nucleus,  if  that  polarity  is  established 
by  the  direction  of  tne  first  cleavage  plane.  The  work  on  such 

orientations  is  very,  limitedjaml  has  often  resulted  in  negative  resuWs 

/  &fy<~MtcJL/$j. ^/S^-iL^f/^^. 

^kjjito<-JT~-\  ^2-c*u)  » woril^U**^  o»   frgflS'9'  eggs 

,'/\  -j^r  |r-  — -  f*± 

-omoryo  QJ  subjecting  *aasQ.o  pressure.  The  spindle  parallel  to  the 
flattened  sides  of  the  egg.  This  is  consistent  with  Hertwig's  theory 
that  the  spindle. should  form  pareifcel  to  the  longer  aocis  ofl  a 
iding  cell.  It  is  conceivable  that  the  power  of  light  to  orient  <*- 
tfe*  spindle  might  result  from  its  power  to  cause  more  rapid  growth 

<-O-^L*^O-£v.   -v-»-v^^-^--T   -*1*u^-«l<"Vl,^  V 

along  one  axis,  with  tho  rtfeult  thayche  elongated  celljin  turn  * 
orients  the  spindle®  No  such  effect  of  light  has  been  demonstrated 


with  animal  eg,^s?  but  in  certain  pi  an  ts .  vi  z . ,  Equi  se  turn ,  Fucus  .Pi  c- 

¥o^v^f(  C/i<-ocxxw<xOc  »* 

fystoseira,,  it  has  been  found  that  one-sided 
'A 

illumination  with  daylight  causes  the  first  cleavage  plane  to  be 
formed  perpendicular  to  the  direction  of  the  incident  light  and  the 
cell  on  the  darker  side  of  tne  spore  to  become  the  rhizoidal  cell. 
Equal  illumination  on  all  sides  retards  or  prevents  germination. 
Gravity  add  contact  cannot  establish  the  polarity  of  these  spores. 

All  these  experiments  were  conducted  witr  natural  light  as  the 
source  of  illumination.  The  first  purpose  of  the  present  investi- 
gation ?/as  to  determine  tne   ower  of  monochromatic  light  to  es- 
tablish the  the  polarity  of  germinating  spores  of  Fucus  evanescens. 

It  was  hoped  that  the  results  o4  such  experiments  might  give  a  clue 

Y>  W 

to   the  mechanics   of   aZuA  orientations. If    all   wave  lengths    should  pre- 

s\ 

duce  the  same  effect  it  might  be  the  result   of  a  general  inten- 
sity gradient;  if  only  the  blue  ligho  is  effective,  the  problem 
is  one  of  a  chemical  effect;  if  only  the  red  it  might  DC  assumed  th*"t~ 


the  orientation  is  due  to  a  metabolism  gradiant.  The  second  pur- 
pose qC&^a  study  of  the  photro*ropism  of  the  young  rhizoids  in 
monochromatic  light.  It  has  been  shown  (^T^jft  that  they  are  neg- 
atively heliotropicjbut  the  apparatus  designed  for  the  polarity 
experiments  made  it  very  easy  to  answer^,  several  questions  concerning 

tnyfr  phenomenon  wore  definitely.  These  questions  are:(j)  What  wave- 
lengchs  are  responsible  for  the  turning  away  from  a  source  of  white 

lightt  (2)  What  is  the  role  of  intensity  of  the  light  or  is  it  a 
matter  of  quality  alone  or  both?  (3)  Do  all  lights  which  have  any 
efiect  at  all  produce  the  same  negr  tive  tropism  profluced  by  white  ^ 
light? 


The  f  irat  work  establishing  the  nov:      km  I  fact  that  one-  - 

sided  illumination  will  cause  the  first  division  plane  of  a  germinating 

J 

spore  to  be  perpendicular  to  the  direction  of  the  incident  light 
s  done  by  Stahl(/f?  $"*)  on  Equi  fee  turn.  He  found  th?<t  the  first  wall 

is  formed  perpendicular  to  •£&  light  rays  striking  the  spores  on  one 
side  only,  and  that  if  ?  11  sides  ore  illuminated  by  rotating  " 


spore?  on  a  clinostat  ,  the  formation  of  ine  vrall  is  retarded  or 
prevented.  The  cell  on  tne  shaded  side  of  tne  s  -ore  become?  the  rhi  - 
zoidalfcell.   in  darkness  the  formation  of  the  first  v/all  follov/s 
no  rule  and  the  rhizoids  extend  4n  every  di  ection.  Stahl  refers  to 

enrlier  v/ork  on  liar  s  i  1  ia  and   n  ara.  whicn  indicates  /I  that  gravity 

a 
is  ton.  controlling  factor  in  the  otientation  of  the  first  division 


A 

plane 


, 
spore  regardless  of  the  light  direction.  SK  ^Je  conclude^  that  no$T 

A 
only  light  but  a  difference  in  the  concentration  of  oxygen  on  the 

two  Fides  of  the  spores  could  determine  their  pol;  rity.  He  says 
that  as  a  result  of  their  respiration  tne  water  in  the  center  of 
the  groups  of  scores  is  lesn  rich  in  oxygenjand  as  a  consequence 
the  rhizoids^p.  are  formed  on  th?>t  side.  Inlsupport  of  this  theory 
is  the  fact  th»  ':.  although  light  can  determine  the  polnrity  of  all 


Rosenvinge(1889)  showed  that  in  Fucus  spiralia  there  is  no 

relation  between  gravity  and  the  first  division  plane  nor  did  con- 

. 
tacf  with  a  solid  body  have  any  effect.  He  got   tne  same  orientation 

- 
to  light  in  Ascophylium  and  ./ucrus'  that  Stahl  did  with  Bfruisetum. 

but  with  puzzling  exceptions.  There  the  spores  were  in  groups  the 

^k_  /T_x£jv«-^W  «-—  *^ 

cell/  toward  the  -4e&r,  interior  of  the  Gr°up  became;  and0  in  the  lov/er 
part  of  hanging  drops  the  rhizoids  appeaWon  the  upper  side  of  the 


/f 

tne  specie^-     led  excet>  Vucua  serratus  ;viz.  .Agcojohyllum  nodosum. 
Fucus  vesciculosus,  J<\  soirniis,  n/.d  Pexvetia  comiii  culrit.p  ,  their 
sensibility  to  light  differs  and  the  oxygen  factor  or  internal  caue~ 

es  t&tjS&Bfe?/  produce  frequent  exceptions  in  all  but  Pelvetia. 
The  rhizoids  of  the  latter  species  are  alwa/y  sf  oraed  on  the  darker 

side  of  the  spore,  and  this  is  the  one  species  in  which  tne  egg 
is  surrounded  by  an  oogonial  wall  which  might  prevent  any  of  he 

effects  of  varying  oxygen  concentrntion^which  can  net  more  potent- 
ly thsn  light  on  the  spores  of  the  other  species.  Rosenvinge  quotes 

Kny  as  finding  that  neither  light,  gravity,  ijor  contract  c?t(  influ- 
ence the  point  of  origin  of  the  pollen  tube  from  pollen  grains, 

but  that  in  tne  neighborhood  of  other  grains  tne  tubelwill  be  sent 
out  from  t,-.'.e  side  away  from  them,  on  which  side  the  supply  of 

oitygen  or  nutritive  elements  would  be  greater. 

-iS^SHSV,  farmer  and  Will  iaias  (  iS'fv  )  state/  that  if  Fucus  spores 

/ 

are  illuminated  on  all  sides  they  tend  to  remain  spherical  in%tead 
of  producing  B  rhizoid  bu  t<:e  elongation  of  one  of  the  two  cells. 
Again(l898)  they  experimented  with  one-sided  illumination  with  the 
usual  result  that  most  of  .he  rhizoids  originated  on  trie  shaded  side 
of  the  spore  and  the  others  *fere  turned  that  Iway.  The  fact  that  some 
graw  out  at  an  angle  to  tne  incident  light  «4s  attributed  to  "the 
character  of  the  egg  itself". 

¥inkler(#//1900)  found  the  some  orienting  effect  of  light  on 
tne  spores  of  Cy  s  t  o  s  e  i  r  a  __b  ar  b  a  ta  but  failed  to  find  any  dffect  of 


a  difference  in  the  oxygen  content  of  the  -vater.  He  too 

A 

that  gravity  and  contact  are  not  factors  in  the  establishment  of 
polarity  of  the  sporelings.  r.e  found  that  the  direction  is  determin- 
ed before  the  firs',  division  takes  place.  Since  t  is  polarity  is 
established  during  the  firstjfour  hours  of  illumination  and  connot 
changed  afterwards  by  any  change  in  the  direction  of  the  incident 
light,  he  concludes  that  light  can  orient  the  spore  only  during 
fertilization. 


-    • 


Randolph  and  I:^rce(l905)  performed  *m£  one-sided  illumination 
experiments  on  Sicbyota.  JJictyooteris.  Lanrencia,  and  Gystoseira, 
and  poinl^out  the  certainty  of  the  j^/diium-jy  action  of  other  factor 


because  rhizoids  are  formed  in  .he  dark  and  in  all-sided  illumin- 
•i 

ation.  They  say  that  although  Y/inkler  (1900)  suggest^  tne  possibility 
of  stopping  germination  toy  changing  the  direction  of  lign-;  every 
three  hours,  i ;  could  not  be  done  with  Sictyopteris.  They  emphasized^ 
theroossibility  of  influences  preceding  the  illumination  affecting 
tr:e  polarity. 

The  work  of  Fronrne'Rev.  1914)  on  the  urediniospores  of  Puccinia 

rhamnif  shauid  oa  men-. ioned  horo/.  He  *&*  that  in  darkness  the 

^  U 

germ  tube  grew  from  any  side^oT  the  spore,  but  that  in  inilateral 

e  tubes  almost  always  issued  from  the  darker  side  of  the  a* 
spore. 


of. 


the  first   cleavage 
icus   scores. germinated  in  u**Tlateral   have   failed  so  far 

™^L^'  _^^  A 


All  attempts  to  solve  thi  groblera  as  to  wh^tr"wave  lengths  of 

;ht  are  responsible  lor  the  orientation 

\ 
plane   o 

^—^  ^ 

and  apparently      -•aTnvalsucceed^fith  the   •  pparatus   described 

in   the   first  port   of   th^>»^pape>>*41owever   it   seems  worth  while 
to  report   t-e  metlpyrfs  used  and  why  theyhmte  failed.    T7ork  v/ill   be 
continued  on^fenis   investigation  at   the   earliest   o*pXjrtunity,  PS   it 
is  mereiar  a     matter   of   obtaining  the  right    conditions   of  "gmjwth 

bejtffnd   the  light  filters,  together  with  a   sufficiently  strong 

illumination. 


The  fruiting  plants  of  Fucus  eyanescens  were  collected  at 
Sausilito  at  low  tide  of  one  day  and  kept  over  night  in  damp  news1*' 

papers.  The  next  mornibg  they  were  dried  slightly  by  exposing  them 
to  the  air  for  about  half  an  hour  or  less.   The  fruiting  tips  were 
then  cut  off  a'^  submerged  in  *ta-  v/ater  in  the  culture  dishes.  After 
fifteen  minutes  many  eggsjand  sperms  have  settled  to  the  bottom  of 
the  dish  or  can  be  scraped  6ff  into  the  water.  The  piece  of  plant  is 

then  removedVnd  the  dish  is  placed  in  the  rack  which  fits  into 
a  dark  box  behind  a  filter  screen.  Each  box  with  its  cultures 

is  placed  at   the  proper  distance  from  the  light  so  that  each  is  il 
luminated  with  equal  intensity.  These  distances  for  each 


the  raethod  by  which  they  -'ere  obtfii-  ed^ 


by  five  as  the  case  might  be 

distance  given  tnei?  however  was  divided  by  four  or 

;      /  *\ 


in  order  to  increase  the  intensity  of  the  illumination  equally 

for  all.  The  illumination  with  the  electric  arc  was  continued 

V—  ^ 

for  eight  in  an  otherwise  darkened  room,  the  carbons  being  ad- 

justed every  five  minutes.  This  time  was  judged  more  than  sufficient 

M*4 


to  produce  **»jseffect   since   it  was  found  in  Cystoseira   ( 


that  the  polarity  of  the  egg  is  so  firmly  established  by  four  hours 

exposure  to  daylight  that   it  cannot  be  changed. 

/      The  f<ct  that  Ku cuy^evan es c ens  is  a  monoecious  specita 
makes  it  impossible  to  tell  the  exact  time  of  fertilization, £• 
but  it  occurs  soon  after  the  eggs  escape  from  the  oogonial 
sac  into  the  water.  The  sperms  at  this  time  can  ba  seen 
escaping  fro-n  the  antheridia  and  swimming  rapio.i./  around  the 
eggs,  then  scattering  as,  presumably,  one  of  than  succeeds  in 
entering.    The  first  oross-wp.li  can  "03  seen  very  plainly 
twenty-  four  hours  after  the  cultures  are  started. The 
mucilage  accompanying  the  eggs  caused  them  to  aether e  so 
firmly  to  the  distil  that  it  is  not  necessary  to  use  f  sol^d 
media  to  ke  p  the  sporelings  from  being  displaced  when  the 

cultures  are  moved  to  the  microscope  sjage  for  examination. 

However  «U-Hha   eggs  germinated  behind   the  color  screens^ 

and  illuminated  for  the  first  eight  hours  after  fertilization. 

- 

showed  4«r  orientation  with  respect  to  the  direction  of  the-  light. 
They  grew  'corually  as  if  in  darkness  with  the  direction  of  the  clear - 
age  plane  following  no  rule  and  the  rhizoids  extending  in  every  dir- 
ection. Evidently  the  intensity  of  the  light  was  too  low  to  have  any 
effect,  or  the  time  or  duration  of  the  stimulation  was  not  right. 

Attempts  to  increase  the  intensity  by  bringing  the  cultures  closer 

that  is. within  about  seventy-five  centimeters » 

to  the  wrcTfre suited  invar iably  in  the  death  of  the  spores  Before  any 

A  placed  (5"cm.  from  the  naked  arc  » 

development  occured.  A  cooling  device^ consisting  of  a  layer  of  water 

A 

(p  cm.  thick  between  two  glass  plates, reduced  the  temperature 
from  29  to  v*s*^y-+*^=^fa^^\\\\\'r^,^f^iFrjrtp^/  but  al so Ar educed 
che  intensity  of  "#Te  light  that  no  orientation  was  obtained. Attempt* 
to  use  direct  sunlight  as  the  source  of  light   also  caused  the  rapid 
death  of  the  eggs,  presumably  on  account  of  ',he  high  temperature 
accompanying  it. 

Future  work  on  this  puoblem  auafr  therefore  involve  the  use 

of  stronger  sources  of  illumination    ajdn  cooling  devices  to 

"-a  an  ^ 


/r 

keep  :;he  temperature  below  the  death  point. 

interesting  results  were  obtained  in  an  experiment  to  dis- 

£#6^4+ 
cover  the  weakest  stimulus  whicu  would  produce  the  charact4ristic 

A 

orientations  of  natural  illumination.  Cultures  were  placed  at  in- 
tervals of  15  cm.  froia  an  east  window  a^n  exposed  8  hours  on  a 
cloudy  day>  Upon  examination  a  few  days  later  every  culture  was-te 

found  to  show  strikingly  the  strong  orienting  effect  of  unilateral 
in 


daylight.  Even  the  one  fartherest  away, 350  cm.  from  the  window^ were 
practically  all  oriented 


c^~«4«j,*     "l^more'dfr  lets^/ 
r._ivery  Culture  js nowing  this  orientaion  has.f  requent  ex- 


ceptions to  the  rule.  Every  worker  on  this  problem  has  reported 
such  exfceptiens  and  they  toave  been  ex*~plained  by  the  assumption 
of  the  existence  of  an  inherent  polarity  which  as  a  rule  i§  over- 
come by  the  stronger  light  stimulus.  The  fact  that  in  absolute  -fr 
darkness,  germination  and  normal  growth  are  as  rapid  or  more  so 
than  in  light,  also  points  60  an  inherent  polarity.  But  the  tend- 
ancy  varies  enormously  in  individual  spores.   Therefore  it  is  easy 
to  understand  that  slight  variations  in  the  quantity  and  quality  of 
illumination  might  easily  produce'-b*^  changes  in  the  ]  sensitiveness 
of  the  spore  toward  light,  which  ;eans  failure  of  experiments  with 
monochromatic  light  until  the  right  combination  of  other  external  £ 
factors  in  produced. 


It  was^oon  discovered  in  the  course  of  this  investigation 
that  although  the  WJLtf  intensity  of  the  electric  are.  used  was  too 
low  to  orient  the  cleavage  plane  of  the  egg  and  too  low  to  cause 
the  cell  away  from  the  ligh  ,  to  become  the  rhizoidal  cell,  it  was 
strong  enough  to  produce  a  conspicuous  neeative  heliotropism  of  the 
rhizoids  of  these  same  spores  if  the  illumination  was  resumed  after 
the  rhizoids  fead  develop  d-  OKly  seven  hour  exposures  were  used  to 


obtain  this  effect.   On  th^day  after  s-ich  illumination  examin- 

ation showed  that  the  rhizoids  of  th_;  cultures  behind  t 

sharply 
blue  and  violet  filters  were  all  turned  away  from  the  light, 

tff/ltr 


behind  -3d*-  t.1'.^  filters  continued  in  the  direction  in  which  the£ 

jtAAJSs™   £*SQ    -4^£~~tt— 

had   started,   .anqpoaring  no  different   thair-&aa   control   in  dark- 

* 

ness.   Therefore  the  wave  IS-ngths  responsible  for  the  neg- 


ative  phototroplsm  ffi////jiin  white  lighyare  those 
of  the  blue  end  of  the  spectrum.  It  should  be  remembered  that  -Hi 
there  is  no  question  of  a  difference  in  intensity  entering  here 
because  each  screen  was  placed  at  such  a  distance  from  the  arc 
that  the  quantity  of  light  in  each  box  qas  the  same. These  re- 
sults are  summarized  in  the  following  table 

..  KELIOTROPISM 

Filter^  COLOR      TAV^  L^CGTH?       DISTANCE  FROM 
,  LIGHT        CULTUPES  NO.  I  +  J 

70  red       6600-7JOQ  A.U.        T&  <~™  . 

71  orange    62^0-6800  '  bff   - 
orange    5900-6200  -rt   - 

yellow    5600-5900  fe>2.  - 

green     5200-5600  70 

blue      4800-5200  (*  %•  " 

violet    4000-4700  •*  "  +         -f 


white     tfo<Jo  -7000  -/- 

^L. 

T  Ke  s  e 

A  Dlmilar  experiment  was  triedVrth  sunligTit;  as"  the  source 


of  illumination.  The  young  plants  were  exposed  behind  the  fil- 
ters all  day  in  a  south  window.  The  same  results  were  obtained 
as  when  the  arc  was  used.  Then  the  experiment  w  :s  repeatedwith 
diffused  light.  The  boxes  were  placed  in  an  east  window  fir  eight 

hours_  ---  10  A.M.  to  6  P.M.  ---  on  March  28.  Again  the  rhizoids 

/i^txz^-d-vt/e-*—- 
in  the  blue  and  violet  light  showed  the  frrMffiisrii,  but  in  addition 


a  considerable  but  much  smaller  portion  ware  affected  in  the  same 


jP  •  J     //   fJui.  c+Ts*s*h£<^^>  f£  <*s<-*-<^££  -* 

behind  the  green  filter.  &******«[<      ,   £->J"Jr<7L  /'   /• 
L  ^JLtZ^^eu^^*^  •+*&*  **^J^* 


waj 

These  experiments  'ndicate  that   the  light  of  wave  length 

* 

4ooo-520CWImgstrom  yUnitaVf^  responsible  for  the  phenomenon, 

but  that  some  rhizoids, more  sensitive,  will  respond  to  those   of 

5200-5600.   It  seems  very  possible  in  view  of  the  results  on 


irolvox  reported  in  the  third  part  of  this  parer  that  with  a^greater  ^ 
intensity,  the  rays  of  the  red  end  of  the  spectrum  might  caWse  the  sane 
negative  phototropism.  •*&? 

Only  the  growing  tips  of  the  Jifrhizofds  are  sensitive  to  light^, 
mhis  results  in  a  sharp  angular  turn  if  the  direction  of  illumination 
is  changed  through  90  or  180  degrees,  or  if  the  plants  be  brought 
from  darkness  into  unilateral  light.  As  pointed  out  by  Loeb  and  others 
tropismJla  uncftubljunliy  due  to  the  di  ference  in  the  speed  of  the 


chemical  reactions  going  in  the  two  dides  of  the  growing  tip. 

The  first  protuberance  of  the  germinating  spore  is  not  affected 
by  light  striking  it  from  th'i  side;  and  if  it  is  so  illuminated 
during  the  early  stage  of  elongation  of  this  cell,  the  first  bend 
occurs  at  the  cross  wall  separating  it  from  the  next  rhizoidal  cell.  In 

s~* 

other  words,  the  firs  t  rhizoidal  /^elongation  continues  in  the  orig- 
inal direction  established  by  the  first  cleavage  plane.  and  the  wall 
separating  it  from  the  next  cell  of  the  growing  ehizoid  appears  as  the 
axis  of  the   tropism. 


In  every  culture  of  Pucus  evanescens  whether  germinated  in 
darkness  or  in  strong  unilateral  light  a  most  striking  orientation  of 
the  first  cross-wall  with  reference  to  adjacent  spores  appears,  ^her- 
e-teer  a  group  of  spores  are  lying  within  about  0.2  mm.  of  each  other, 
the  first  cleavage  plane  is  perpendicular  to  the  direction  of  the  cen- 

t^er  of  the  group.  THe  cell  toward  the  interior  invariably  becomes 

C    ) 

the  rhizcidal  cell.  This  phenomenon  was  reported  by  Fosenvinge  in 

--" 

other  species  of  Fucus  and  in  Ascophyllum. 

^ 


A  study  of  this  phenomenon  ^pfs  madeM'to  determine  the  strength  , 

compared  to  *^'**^' 


of  the  stimulus  producing  this  effect,  *«*-  that  of  light.  in 

A 


A 


orientation  lu  lh  )  lUnaaliou  of  itc  rayo.lt  was  at  once  very 


evident  that  for  most  spores  the  formal?  provaiirs  when  the  spores  are 
within  a  short  distance  of  eachf  other  ---  .2  mm.  or  often  more  --- 
and  beyond  this  distance,  the  chemical^)  stimulus  becomes  too  weak 
and  only  the  light  is  able  to  determine  the  polarity  of  the  plant. 
Only  the  comparatively  isolated  spores  therefore  ever  show   the  orient- 
ation to  light  ;i-rrj  )i  I'JL  I'H-iml  »  with  the^ource^  of  illumination  uned 

here. 

The  phenomenon  is  V3ry  conspicuous   ia  groups  o"'  2,  3,  or  4 

eggs  as  well  as  in  masses  of  fifty  or  a  hundred..  In  these  1  ,rge  ,-roups 
it  is  made  evident  by  the  invariable  rtile  that  no  ;%fl/^/rhizoid  ever 

extends  outwards  from  a  group.  Then  two  spores  are  within  the  distance 

which 
through  the  stimulus  is  effective,  the  first  cleavage  planes  of  the  two 

are  often  parallel  and  the  rhizoids  grow  towards  each  other  and  often 
meet  tip  to  tip.  The  groups  of  five  or  six  often  make  symmetrical 
star-like  designs  when  the  rhizoids  have  grown  and  p/oject  beyond  the 
group. 

""he  spores  are  more  rarely  affected  in  thas  way  when  the  distano^ 
between  them  is  over*>.3  mm^but  the  phenomenon  is  sometimes  observed 
in  spores  as  much  as  O.5  mm.  apart.  Tithin  a  distance  ofo.2  mir.. 
there  are  practically  no  exceptions. 

^he  relative  sensitiveness  of  a  sj  ore  towards  light  and 
towards  this  cherr.ical(  ?  )  stimulus  varies  greatly  for  different 
spores.  "'hen  cultutes  were  placed  in  the  window  to  get  as  strong 
a  light  stimulus  as  possible  in  order  to  determine  at  what  distance 
from  each  other  the  eggs  had  to  be  not  to  show  a  greater  sensitive- 
ness towards/the  chemical  stimulus  than  towards  the  light,  it  was  found 
that^this  distance  followed  no  rule,  the  scores  showing  the  greatest  in- 
dividual differences.  Of  two  spores  lying  within  0.3  mm.  of  each  other 
one  might  be  ^entirely  oriented  by  the  adjacent  sporephile  the  otherj 
apparently  like  it,  Would  show  only  the  action  of  the  light  stimulus. 


In  many  canes  two  such  spores  wouljl  see-  to  show  a  rss-iltant  effect 
of  the  two  stimuli  so  that  both  -YOU Id  be  half  turned  towards  each  other 
with  fe£*VhlzOidal  ceil«  showing  a^tcTtake  -a  direction  away  from  the  - 


•££oK-  iv*~-*  •  — 

light  at  »  resultant  angle. 

T  osenvinge  ascribes  this  group  orientation  to  a  difference 

d>n  the  concentration  of  oxygen  or  of  nutritive  substances  on  the  two 

forms  on  th >  side 
sides  of  the  spore.  He  thinks  the  rhizoid^i'/  4,/V/1/  toward 

of  a  group  or  towards  another  egg  because  the  water  on  that  side  is 
less  rich"  than  on  the  outer  side  of  the  spores  as  a  result  o,'  their 

/\  £**u^A. 

metabolism,  '"inkier  (^  ) working  with  Cystoaeira  barbata^that  a  dif- 
ference in  oxygen  concentration  ha?  no  such  effect. Apparently  the  phe- 
nomenon does  not  occur  naturally  in)thisjspecies  since  Wwr  figure 
given  shows  nothing  but  the  effect  of  light. I  have  nevor  seen  a  culture, 
of  Fucus  evanescenjlth  spOres  germinating  so  near  each  other, which 
s!  owed  only  light  orientation  and  ::ot  the  group  orientation.  aAl- 
raost  invariably  when  the  spores- of  this  species  germinate  in  such 
close  proximity, lipht  appears  to  have  no  power  to  establish  the  po- 
larity of  the  plant. 

The  possibility  that  the  group  orientation  is  due  to  a  pol- 
arity established   by  the  position  of  the  egg  in  the  oogoniura  is 

tut*** 
suggested  by  finding  many  groups  of  lying  just  as  they  escaped  fror- 


the  oogonial  sac  and  conspicuously  oriented  with  respe?t  to  each 
other.  The  fact  that  groups  of  ten  or  of  two  are  as  regularly 
oriented, would  refute  thT  suggestion;  but  in  order  to  prove  that 
the  phenomenon  is  the  resuljr  of  a  stimulus  acting  after  the  eggs 
leave  the  oogonium,  a  group  of  them  were  transferred  to  a  watch  crys- 
tal and  mixed  with  the  point  of  a  needle  until  their  relative  posi-fc- 

"/ions  were  entirely  changed.  But  when  they  germinated  the  character- 
istic orientation  with  respect  to  each  other  was  found  to  be  with- 
out an  exception. 


mhe  only  apparent  explanation  of  the  group  orientation  is  '.hat 
of  a  diffusion  gradiant  of  some  substance  emanati^ng  from  a  growing 
spore,  or  of  some  substance  being  used  up  by  it.  A  continuation 
of  the  inve/stigati  ^n  of  this  problem  will  b3  an  attempt  to  dis- 
cover a  substance  or  substances  which  can  so  effect  the  dividing 
nucleus  of  the  egg  cell  that  its  unequal  distribution  on  *M  sides 
of  the  cell  will  orient  the  qxis  of  the  spindle,  The  effect  of  bub- 
bling carbon  dioxide  or_  oxygen  through  one  end  of  a  culture  will 
be  tried  as  being  the  most  probable  factor^  involved. 

A  striking  phenomenon  which  seems  to  be  further  evidence  of 
the  power  of  a  chemical  stimulus  to  orient  the  spores  was  found  in 
three  different  cultures.   ?.mall  pieces  of  a  foreign  substance, 
apparently  sand,  caused  the  orientation  of  the  spores  adjacent  to 
•astey'ith  the  result  that  the  rhizoids  all  extended  inward  towards 
t:  e  substance.  This  material  was  present  in  too  small  amounts  for 
chemical  analysis.  A  search  for  some  difficultly  soluble  substance, 
or  an  insoluble  substance  which  might  be  sligBiJfly  soluble  in  the 
weak  carbonic  acid  produced  by  the  growing  spores,  which,  when  added 
to  the  cultures  ,  might  orient  the  eggs  adjacent  to  it,  has  failed 
to  brin*  any  positive  results.  They  do  show  ^however,  that  the  phenom- 
enon is  not  due  to  a  contact  stimulus.  "Ehe^//^  substances  tried 
W3repcheelite/  Ca^o^Oj;  'Magnetite/  FQj0J,  Ba  ite/Ba^So),  Casser-ite 

n  oAnornblend,  tfubellite,  beach  sand,  granite,  and  silve~r  filings. 
The  substance  or  condition  originating  in  the  activity  ofacfjacenf 

spores  which  has  so  powerful  an  effect  in  orientating  the  first 
plane  and  in  determining  which  cell  shall  become  the 


A 

zoidal  cell  has  no  power  to  cause  any  chemotropism  of  the  rhizoids 

after  they  are  started.  No  rhizoid  has  been  found  to  have  its  direct- 
Ti  on  modified  by  the  presence  of  other  spores  adjacent  to  it.  In 
the  absence  of  any  light  s$imulus)the  rhizoids  continue  in  the  direc  - 
tion  that  they  take  priginally  from  the  spore. 


-i-Ct^Yrt/ma/W 


TO  summarize  briefl"  '.  .is  work  on  light  and  chemical  stimu 
li  as  they  affect  the  polarity  of  ^ucus  e      .d  the  direction  of 
growth  of  the  rhizoida: 

(1)  Green,  blue,  8$rt  violet  "-ight  (4000-5609  A.n.)  of  an  inten- 
sity great  enough  to  produce  negative  phototropisms  of  the  growing 
rhizoids  is  without  effect  on  the  direction  of  the  first  cleavage  f 
plane  of  the  egg. 


3 


?N 
>  J 


chemical  stimulus  which  orients  the  direction  of  the 


first  cleavage  plane  and  determines  which  cell  shall  become  ths 


rhizoidal  cell 


alli 


diet 


vhemi 


'  ~-'  hrig   no      power   to  •^s&r,.      c  cf 


rhizoids  . 

(£)Th    laxative   photctropism  or  the  rhizoicr  :  .  *i  .^o- 

.«.  ~  c  '  _        .     '.  .'       ,  .  "^  "  .a_.  ^       13 

since,  with  equal  intensity  of  illumin;  ."  ;ht 

•  :  peel  .          Lthoti  ^ 


j  - 


—244. 


V.    --  Pho tot rop isms   ci    Volvox   in  Mono chro 'na tic 
Light  of  Equal    Intensity. 


Oltraanns    (  /?<fR ) ,    Holmes    (  J<p3 )    and  Mast  have    reported  in   detail 
the  reactions   of  Volvox   to    li^t   stimuli.        No  one,    however,    has   studi- 
ed    its    response   to   monocnroraatic   illumination.        The  purpcs     of   the 
present   study    is   a   comparison  of  its  phototropisrne  in   different   spectral 
re -ions    for  which    the   intensity   is  made    equal. 

The  recent  article  by  Mast    (l?'7)    suns  up   in  a   table   the  litera- 
ture on    the   reactions   of  plants   and   ini^als    to    colored  light   so    cc    - 
pletely  and   so    concisely    that   there   is   no   necessity   for  a   repetition 
here.        ite   summarizes   briefly    results    jiven  in    the   table   as    follows: 

"For  seedlings   <•  f   gr  5  »n  plants,    plumules   and   radicles,    the 
region   in    the   spectrum  of  maximum  stimulating   effect   ia    in    the   blue 
or  violet.        For   the  fungi    it   is   somewhat  nearer   the   red.        For  Bac- 
terium pho  tour?  tri  cum  it  is   in    the  infra-red  and   the  orange.        For 
Oscillaria  and  Piraiaeoium  bursaria   is   it   questionable,    activity  and 
aggregation  being  probably   determined  by  cuemioal    changes   in   the   solu- 
tion  associated  with   the    colors.        For  Chlp.mydomonas   it  is   in    the 
green;    for  all   r  ther  unicellular  forms    tested  it   is    in    the   blue,    as 
it  is  also    for    the   co^l^nterates   and  vermes   and   for  a  few  of   the 
molluscs   an.-"1    Arthropods.          >ut   for  most  of   the  molluscs   and  arthropods 
it  apcears    to   be   in   the   ,^re ^n  or  yellow." 

T   -)t    tb  ?  -:if<st   effective  wave  lengths   -ir*3  not   the   erii.ie    for   even 
related   forms    in    the  low«r  organisms    iB   furt)i«r  borne  cut  by  lias  Us 
(   l^l"[)    results.        ue   found   that    the  maximum  efficiency   is   near  483 
for  3uglena,    Tra^relomonas,    Phacus,    Gonium,    Arenicola  and  Lumbric.s; 


—25-- 


near  524 /y    for  Pandorina,    Eudorina  and   Spondylonio  ruin; and  near 
503u./^-  for     Chlamydoinonas   and   olcwfly   larvae.        The  wor?    of  Schaelferf^     ) 
on  amaebae     3    i  iteresting  as  his    results   indicate   that   the  prw»r  cf 
a  beam  of  red  light   to    cause    the  organisms    to   move    towards    it  is   as 
great  as  a  beam  cf  white  light,    and  hae  mere  attraction   than   the   blu»- 
Most  investigators   of  phc  to  tropisms    find  either   that   the   red  is   less 
effective   than   the  blue  or  that  it  has  nc    effect.        A  few  find   that 
in   equal    brii'Jitness,    tha   effect   is     nearly    the  same   for  all    colors, 
e  Volvox  colonies   upon  which    the   following  experiments   w~r 
made  wre   collected  by  Dr.  N.   L.    Gardner  in  a  small   la>e   in  Golden 
Gate  Park  on  April  2,    1918.        They  we*e   so   abundant   that  the  water 
was   quite   :Tr?«n  vrith   them. 

On  April   5    they  were   exposed   to   direct   nunlifiht  behind   the 
seven    Vfrat '.en  litfit   filters   used  in   the  work  on   iucus.        The   same 
rectangular,    flat-aided   dishes  made  of  microscope   slides   cut  and   ce- 
mented  together  were  used.        The   disfcss,    filled  with  a  Vclvox    -us- 
pension  were  planed  in   the   dark  boxes   in  one   end  of  erioh  of  wliioh  a 
color   sere  ?n  waa    fitted.         The   series  of   eight  boxes   were    tnen    ex- 
posed to   direct   sunli.-jit.      A:   intervals    the   covers  were   raised   to    de- 
termine  roughly    the      ^r^ntage  of  org'inisns    reipondinst    as   shown   by 
the   completeness  of   thei  c  aggregation.        Ths   results   of    Uiis   series 
are   surnra-'xrized  below,    the  plus    ^i  ,hs    i    •:! opting  an  obvious   positive 
hello  tro  pi  am  with    Uie  org  nip-in    coll  e  -ted   against   the   ^lass   on    the 
side   toward   the   sun,    a  2<=>ro    indicnti".;r  no    ^vidence  of  any  eftect  of 
the  light. 


--26  — 


Table  No.    1. 

Volvox  Reactions    to    Sunlight  behind  Wratten   Colored  Filters. 


Filter 

70 
71 
72 
73 
74 
75 
76 

Control. 
Table  No.    2. 
70 
71 
72 
73 
74 
75 
76 

Control. 


Wave  Length   in 
Angs  t  r  o  m  un  its. 


-  7000 


3~c[  OO    —  (o^OQ 
5<o  oo  -  y<?o° 


4-700   - 

4-066  47OO 

H-  o  o  o    — 


QO  - 


-    (c^OO 
5(0  00     — 

s'Zoo    -    ^6,00 


y-ooj 

Lj-Odi)    —     JOOO 


Color 


y£  ) 


Sxposure 


y  ' 

10' 

%o 

T       IT 

r    IE 

r  IT 

o.o 

-1-    o 

f-  ° 

o  o 

0      0 

-f    o 

0    0 

0      0 

0     CP 

+  t 

4-    -f- 

r  t 

f-  + 

4-   -f 

t   -f- 

i-  t 

t    + 

t    t 

+  t 

t    + 

4-    t- 

+  t 

-h    i 

t    f 

t 


3"  ' 

jo 

i  sT 

^ 

_ 

JO 

O 

o 

O 

o 

' 

0 

<^ 

0 

•f 

t 

O 

o 

o 

f 

t 

* 

* 

t- 

f- 

-f- 

t 

,h 

f 

t 

t 

-h 

f 

f- 

1- 

-j- 

-f- 

* 

^ 

t 

-h 

•f 

± 

f 

f- 

t-  . 

Table   1   shows    that  wave   lengths    from  4000    to   4700  A.    are   de- 
cidedly more  powerful    in   directing   the  movements   of  Volvox   than  are 
those   of   the    remainder  of   the   visible   spectrum,    4700   to    7000   A.    U. 
There   is   an   indication,    however,    that  some   individuals    respond    to    the 
long  waves. 

Table  2   shows    that    the   stimulating  efficiency   of   the   difierent 


—27-- 


is    dependent  on   the   duration  of   t;:e    exposure.        At   the    -^nd  of 
only    three  minutes,    the  organisms   of   the   gre«n,    blue  and  violet  were 
all   over  to    the  brighter    side  of  the   dish.        At    the   end  of  15  mi-iutes 
the   red,    orange   and  yellow  had   still    oroduced  no    visible   effect.      But, 
after   20  minutes,    all    but    the   longest  waves,    6600    to   7000  had   caused 
a   definite  ag  regation;and  after   thirty  uinutes,'    the   effect  was   se^n 
benind   this    r^d  screen. 

As   striding  a?    tnis    relation  of    the   time   factor   to    the  power 
of  light   stiumli    to   produce    the  phc totropisrn  was    the   difference   in    the 
response   behind   the  'four   filters   of   the   green,    blue,    and  violet.    After 
only   3  minutes   of   exposure    the  aggregation   effect  was  most  marked   in 
the   violet,    less    in   the  blue   and    still   less   in   the   green.        The 
difference   in    the    appearance  of    the    four   disnes  was    due  to    the 
difference   in   the  number  of   individuals    that  had   responded  positively 
and   the   completeness  of   their   response,    i.e.    in    4-0 o-j  —  i+j  o 
practically   every    colony  -va«    igainst   the  glass  on   the  outer   side  of 
the   dish;    in    A  =.  *f  9o   - frffctf  ^- A0       there  were  more   scattered   about   in 
the  water.        In  5200    -  560^tf still  more  and  in  560    -  590^ 

there  w»re  just  barely   enough  affected   to  make   it   evident    that   some 
were  positively  «[z?«o%4'(l;        After   10  minutes    this    gradiant  was    still 
visible.        After   about   15  minutes,    the   dishes  all   looked  alike.      Tnis 
again    shows    the   importance  of   the    time   factor,    since   the  less   sensitive 
organisms  which   respond  less    rapidly   are  after  a  longer  time  afteoted 
to    the   sane    decree. 

In  all    the  succeeding   exposures   with  sunlight   this    rule  held 
good,    that   the  organisms   behind     76snd75    respond  most   rapidly   and  most 


--2;  -- 


crrnpletely ,  followed  "by   those  "behind  74    and  then   73.        It  WT.S   <  f oen 
quite  impos   ible   to    detect  •  ny  dit'terenoe   in   the   response  behind  75 
and  76. 

It  was  noticeable   in    every   series    exposed   that   in    the   -vhite 
light  of   the    control   complete   aggregation  of   the    colonies   as    the   re- 
sult of    their  phototropism  was  no*-   so    rapid  as    in     A=*tof-i^o  /*-P- 
Repeatedly    the   observation  was  made   that    the   control   locked  more  like 
the   culture  in     fr*1-  VR»  /+yt^  •        T:.e   expl.-unticn  in  prob-ibly 

either   that  the  intensity  was   fso   raiich   greater    that  some   individuals 
were   caused   to    respond  negatively,    or  were  neutral;   or    that   the   great- 
er  reflection   from   the  back   of   the   dish  ma  e   all   parts  of   the  wat»r 
more  nearly   ali>-e  in   intensity  of  illumination  and  so    tended   to 
equalize    the   Rtiraulus   acting  on    the   different   sides    cf   the  orginism. 

When  a  series  of   cultures  was    »xpooed  in   the   same  way  with  the 
sun  hidden  by   clouds  no    respcns  ->  could  be  obtained  behind   the   red, 
cringe   ^nd  yellow  filters. 

Theae  experiments    srow   the  greater  stimulating  eiticiency  of   th  e 
blue   end  nf  the   apectrura   since   comparison  of   the  order  of  efficiency 
of   the   screens    in  produciri/-;   the  positive    response  is  not   in  agreement 
with   the  order  of  the   intensity  of   the  light  behind   them,    (see   table  1  ) 
In   fact    the   stimuli  of  least   energy  produce   the  most   rapid   response. 
They   also   show    that  with   a  longer   exposure  or  more   intense  stimulus 
the  less    effective  wave  lengths  may  produce   the  s-ime   degre  "•  of    r  spons  e* 
In  none  of    the    exposures    to    sunlight  were   there  any   negative   reactions 
or    reversals  of    the    response. 

On  April   6,     the   experiments   ^«re    repeated  -vith    the    electric 
arc  as    the   source  of  li  ht,    and  with   the   dark  boxes   at  such  distances 
from   it   that   the   intensity   behind  all  was    the  same.       The   results   are 


--2S-- 


as  follows: 
Filter 
70 
71 
72 
73 
74 
75 
76 


Wave  -^-'n.- 

(.(.oa  ~     "7 °0  & 

b  1(1  O      -     &  %  00 

ac,  -    *> 


Color 


Distance 


osure 


AJL 


CJ 


+• 


H  y  oo    -  5  ' 

^   0    6  0       ~    Lf   -J  u0 

-  -i000 


ft. 

r 


r 
t 

t 


f- 

t 

1- 


The   ri.pid   reBpcne--   in.    t>m    re'.  v;s   aurpriging   sinoe   the   energy 
must  have  be-n  leea    '.han  in   sunlight.        It   took  20  minutes    to   get  a 
noticeable    reaction   in    -Jie  orange  and  yellow  in   sunliriht    the  day  befor 
Here  with   the   arc   as   a  source   of  light   it    took   hut   thr°e  minutes. 
It    toc-y   30  minutes    to   get   the  resporv  e   in   the   red    that  was   produoed 
by   the   arc   in   5  minutes.        The   explanation  rni^ht  be   that   the 
colonies  were  niore  sensitive   to    light  nn  April   6.        It  was  unfortu- 
nate  that    tjiis   day  vrae    oloudy    so    that   the    experiment   -*ith   sunlight 
o  uld  not  be   repeated.        That    the  ability  of   the   colonies    to   re- 
spond  is   dependent    to    a  large   extent  en   their  own  condition  as 
aflected  by   external   factors   of    their  invironment  was   shown  striking- 
ly by   the  fact   that  organisims  kept  over  night   in  a  small  mouth 
bottle  -vould  not   respond   to    -my   lirjit  stimulus,    while  o  th-TS  cf   the 
same    collection  ?ept   in   shallow  pans    reacted   rapidly.      Mast    ( 
found    considerable   difficulty   in   ,;etting    consistent   responses  on 
account  of    the  gre    t   change   in    the   reactions  of  .  is   organisms  with 
Change   in    their   con di  lion  due   supposedly    to    the   li,  ht  and   temp  ^r-s 
oonditons. 


—30-- 


ism,        Also    it,  J.B  prob-'.ble   in  vi-^w-of  jLoab^s  -vor>-    (1^6  )    that   the 
phototropio    reactions  of  all   organisms    change  with   their  age. 

Another   explanation  which  was   suggested  by   the    fact  that 
white  light  was   often  slower  in  producing  a   response   than    the  b  lue 
and  violet,    is    that    the  greater   energy  of   the    red  in   sunlight  might 
have   tended   to    reverse   the  positive   reaction  or  neutralize  it;   or   it 

ight  h-iv*  be<?n   so    reflected  within   the   dish  as    to    act  more  nearly 
with   the  optimum   intensity   on    -<11   sides   of   the  organism.        •"»    that 
as   it  mri.y,    the   fact   remains    that   repeated   trials  prove    Conclusively 
that  at   the   end  of  a  fiv-  minute   exposure,    all   wave   lengths  of     the 
visible    centrum  hnve  produced     equal  eft^ots   when   the   source  of 
li;Tht   ic    the   electric  arc.        This    is    further  proof  of  Mast's    Wf  ) 
contention    tir.it:          "There   ia  nc    evidenc--    i-.-Mc   ting   that   stimula- 
tion  i-,    n.:r;    of   the   •  3    studied   is    independent  of  lurranous    in- 

tensity,   for  if   the  light  in    the  spectrum  on    Cither  side  of   the  maxi- 
mum be  made   sufficiently   intense   it  becomes  iaore  efi  active   than  at 
the  maximum,  M 

On  April  20,    another   collection  of  Volvox  was  made.        It  was 
ho  r;ed   that  a  rough  approximation  of  applicability  of   the   Roscoe- 

Buns>?n  Law  in   the    reactions   of   th  is  form    U>   li  :ht.        This   law  states 

•ing 
that     o'J<-r   conditions   "be/eqial,    the  product  of    the   intensity  and 

the  duration   of   the   exposure   Is   .'?    co  .stant.        Owing,   however,    to    the 
short   time   required   for    response  and    the   variations   in    the   sensitive- 
ness   of   individuals  making   it   impossible   to    determine   the    end  points 
exactly  no  thin-   c  ,n  be   concluded  o.s   to    the  truth  of   this    law  for 
Volvox  u    Li]    .  nr?   RQ   urate  ra^ans   of  ..leosuring   the  b  'ginning  and   end 
of   the   reactions   is  obtained.        To    show  the   diilic^lty  produced  by 


—51  — 


th«        i  :}-    responses  of    the    colonies, -..he    tira"   taken   for  most 

individuals    to    ^rosa   the   dish,    i.  e.  ^'  .;a».. ,    in  white  li.'ht   bO   om. 
from   the   source  in  a  straight  line   towards    the  aro  was   about  1 
minute.  ?n   this    distance  was   doubled,    the    time  was    still   about 

1  minute.        When   the   c  Iture  was    re::.cved  200    om.   many    c  lonies    still 
requii-ed  rrily   1  rainu^e   to   get  icroes    Uie   dish. 

This    effect  of   Changing  the   distance  was    repeated  with    the 
No.    70   filter,    since  as   it   transmits    the  longest  wav~  lengths   the 
time  cf   the   reaction  nhculd  be  longer.        However,    they  were  still 
too    n.^.rt   to   obviate   tho  lar.je   errors   due   to   the   indefinite   end 
points.        At  a   distance  cf  25   cm.    Lhere  was  a  noticeable   collection 
on    tiie   li(shter   si    3  of   the    dish. After   13  minutes   nearly   all  had  moved 
over.        At  a   distance  nf  50   cm.,    ICO   cm.,    :»nc  200   cm.,    the   same 
positive   reoulte  v/    re  c^  'ith  t>ie   five  minute  exposure.      Al- 

though  failing   to    si:ow   the  applicability  of   the  Rosooe-Bunsen  L  w 
this    exp^riniont   r^.cws    th<;  potency  of  the  long   red  rays    to    oause   the 
same  pro  to  tropisms   produced  by   the   blue  waves   when   they   aot  with   the 
right  intensity. 

~:ry   exposure    througiiouc,   tli^-^e   experiraents  was  made  with  a 
fresh   culture   BC    t.-at   in  no    inst  nee  was    tiiere  a    ch.ince  of   the 
sensitiveness  being   ..ifior^nt  for   the  succeaaive  exposures  because 
of   the   of -fact      I  -ceedint:;   illumination. 

•  j    (^9o3)    reports    that    tiie  positive  p}:ototropism  in 

medium  li'jht  is    reversed  by   strong  light.        Att-=>mpts  w^ro  made   t): ere- 
f  re   to    find   the   turning  point   for   each  screen   by  .lessening   its      is- 
tan*5e   fro^i  the  aro.  *t    the   control   behind   clear  glass  was   the 

only  one   in  which  any  negative  pho to t ro ;: i 3in  could  be  obtained   nnd   the 
response   M -re  varied  at   different   times.        In  one   experiment,    the 


—32-- 


orgaii^ms   reacted  positively   at  40   cm.    from   the  aro,    negatively   at 
20   cm.        In  another,    the  neutral   point   seamed  to   be   50    cm.    away. 
Quite  often   Tit   this   distance    there  were  nearly  as   raany   colonies 
swimming  away   from  as    towards   light.        The   response  wis   always  more 
definitely  positive  at  100   om.    than  at   50    era.        Sometimes,    however, 
the   response  was  mrstly  positive  as    close  as   10  om. ,    so    that   the   re- 
versal  is   dependent  to   a  large  extent  en    the   -cndition  of   the  org'-n- 
isms   as    for    the  other   screens,    the   greatest   intensity    obtainable  be- 
hind any  was    too   low   to   produce   any  negative   renuonse. 

An  entire   carbon   aro  run  was   projected  on   one   dish  of 

organisms.        By  looVing  down   it   could  be   seen   immediately   that  while 
those  cr£T.nir»"3    fin  din  selves    in    the  yellow,    ^reen,    blue  and 

violet  lip;ht  swam    LowirdH    the  litf-.t,    these  of  the    red  waved  not   to- 
wards  the   front  of   the   dish  but   in  a  direction  por.^ii^i   to    it,    i.e. 
towards    the  yellow.        The  yellow  apr.eared   to    the   eye    the   Brightest 
part  of   the   dish.        The  organisms   in   it  were   dcubtless   decidedly 
photo  vronic  boc-'i-se  of   the    relatively  greater  intensity,   while   those 
of   the   blue  were   so   in  almost   equal    degree  because  cf   the  greater 
ef f ectiveneflr*   of    these  wave   Tr-«n;-:tr.8   even    ^ t     low   intensity.      In    the 
red   the  intensify   wna  not  gre   t   en<  ugh    U)   overcome   the   ineffectiveness 
of    the  lon/3   r;iys,    30    tiie  organisms   responded  either  to   an  intensity 
gradiant  whi  oh  led   them   towards    the  yellow,    or   to    •>   wave  length 
gradiant  which  would  also    lead    tnen  toward   the  yellow.        Or   the    r   - 
suit  might  have  be-=>n  due   to    a  diffusion  of  the  more   ei-:iri«nt   rays 
into    the    red.        The  raraa   red  rayp    in    th<5  naVed  aro   exposure   th«re 
was  no    -iefl -ntion  of   the  pat!"!  leading   dire^t-ly    toward?    the   source  of 
light. 


--33-- 


It   is    interesting   in    this    connection    to   note  Holt   and  Lee's 
)    conclusions   as    to    the    vole  of    the   intensity   factor   in  phcto- 
tropis      .        They   ntate    that,    "T'n^re   is  no    evidence  t/iat 

• 

respond   to   any   other  property   cf  li^ht    than   its   intensity.        All 
phototatio      response   in    ^xplainea   by    the  ii  tensity   of   the   11,-^rt,    and 
the   direction   fro;a  wai ^Ji   it    -lornes.11        But  my   experiments   'Vith  Volvox 
show   oonolu'9ively    t/iac   for   Any   Driven  intensity    the  blu3   and  violet 
wave   lengths  tire --test   stim  luting   effioienoy,    but   tliat  by 

increasin-;   th-j  duration  of   the   exoosure   the  same  effect   is  produced 

Ln  d  tlie   otli«r    BCte^naJ    and  "by   ,  aity  of   the 

other    colors    they    oan   be  made    to   produce   an   equally    rapid    re  ponse. 
This    is    in   in   or     a  i     .  1  -.c-'t's    ( '^'7   )    Conclusions    that  photo- 

tropio    resp'-na-jB   are  net   entirely    in  ependent  of  intensity. 


•  • 


NON-CIRCULATING  BOOK 


783071 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


